1. Field of the Invention
The invention relates to an improved total heart prosthesis.
It relates more particularly to a small size total heart prosthesis with a single activation source for the right and left ventricles, having a functional geometry which is a close as possible to the functional geometry of the natural heart and which reproduces the hemodynamic functioning laws of the natural heart, in particularly STARLING'S law and SARNOFF'S law.
2. Discussion of the Background
A prosthesis of this type which has shown itself to be satisfactory in operation, not only during tests in vitro but also tests in vivo on animals is divulged in FR-A-2 446 631. It comprises a case implantable in the pericardial cavity and the geometry of which is very similar to the geometry of a natural heart with, inside this case, a motor device essentially formed by two membranes one of which works during the elongation stroke within a space defining the right ventricle and the other of which works during the deformation stroke within a space defining the left ventricle, the motor device acting respectively on blood bags enclosed in the right and left ventricular spaces. The blood bags are adapted to be connected to the vessels of the circulatory system of a patient by means of valves mounted in valvular orifices formed in the case of the prosthesis, the latter being actuated by means activating the motor device such as an extra-corporeal pneumatic energy source or an electric motor with implantable battery or an electric motor controlled by a nuclear energy source etc., with servo loop means for regulating the blood flow.
As described in the above patent, the membrane of the right ventricle of the prosthesis, with which a support is associated, is an elastomer material membrane subjected to alternate elongations during a very large number of elongation-deformation cycles so that, after several tens of millions of alternating movements, alterations may appear such as micro-cracks which, in the long run, may cause its destruction.
Therefore the problem arises of providing a total heart prosthesis of the above described type, in which the membrane of the right ventricle has a lifespan as long as possible, in any case greater than two hundred and fifty million cycles and which, however, satisfies the other conditions imposed on the motor device of the prosthesis, in particular ensuring for each pulsation the ejection of a volume between 60 and 90 ml of blood. Considering, on the one hand, that for a membrane having a certain area, this useful volume is directly related to the elongation of the membrane and that, on the other hand, the maximum elongation conditions the number of cycles to which said membrane may be subjected without the appearance of micro-cracks, the problem which arises is then that of providing in the motor device of the prosthesis a membrane arrangement ensuring the desired volume variation for an elongation as small as possible.